function [msg,x,y,nfft,noverlap,window,Fs,p]= specchk(P1,P2,P3,P4,P5,P6,P7)
%SPECCHK Helper function for SPECTRUM
%	assumes that there are between 1 and 7 arguments on input

%	Author(s): T. Krauss, 4-6-93

if 0,   % forces the interpreter to pass parameters by value, not reference
    P1=P1; P2=P2; P3=P3; P4=P4; P5=P5; P6=P6; P7=P7; 
end

msg = [];
if (nargin>1),
    if all(size(P1)==size(P2))| max(size(P2))>1,   % 0ne signal or 2 present?
        onesig = 0;      % two signals, x and y, present
        x = P1; y = P2;
        for k = 3:nargin,    % shift parameters one left
            eval(['P' num2str(k-1) ' = P' num2str(k) ';']);
        end
    else 
        onesig = 1;      % only one signal, x, present
        x = P1; y = []; 
    end
else  % nargin == 1
    onesig = 1;      % only one signal, x, present
    x = P1; y = []; 
end

% now x and y are defined; let's get the rest

if nargin == (1 + (1-onesig)),
    nfft = min(length(x),256);
    window = hanning(nfft);
    noverlap = 0;
    Fs = 2;
    p = [];
elseif nargin == (2 + (1-onesig)),
    if isempty(P2), nfft = min(length(x),256); else nfft=P2;     end
    window = hanning(nfft);
    noverlap = 0;
    Fs = 2;
    p = [];
elseif nargin == (3 + (1-onesig)),
    if isempty(P2), nfft = min(length(x),256); else nfft=P2;     end
    if isempty(P3), noverlap = 0;  else noverlap=P3; end
    window = hanning(nfft);
    Fs = 2;
    p = [];
elseif nargin == (4 + (1-onesig)),
    if isempty(P2), nfft = min(length(x),256); else nfft=P2;     end
    window = P4;
    if length(window) == 1, window = hanning(window); end
    if isempty(window), window = hanning(nfft); end
    if isempty(P3), noverlap = 0;  else noverlap=P3; end
    Fs = 2;
    p = [];
elseif nargin == (5 + (1-onesig)),
    if isempty(P2), nfft = min(length(x),256); else nfft=P2;     end
    window = P4;
    if length(window) == 1, window = hanning(window); end
    if isempty(window), window = hanning(nfft); end
    if isempty(P3), noverlap = 0;  else noverlap=P3; end
    if isempty(P5), Fs = 2;     else    Fs = P5; end
    p = [];
elseif nargin == (6 + (1-onesig)),
    if isempty(P2), nfft = min(length(x),256); else nfft=P2;     end
    window = P4;
    if length(window) == 1, window = hanning(window); end
    if isempty(window), window = hanning(nfft); end
    if isempty(P3), noverlap = 0;  else noverlap=P3; end
    if isempty(P5), Fs = 2;     else    Fs = P5; end
    if isempty(P6), p = .95;    else    p = P6; end
end

% NOW do error checking
if (nfft<length(window)), 
    msg = 'Requires window''s length to be no greater than the FFT length.';
end
if (noverlap >= length(window)),
    msg = 'Requires NOVERLAP to be strictly less than the window length.';
end
if (nfft ~= abs(round(nfft)))|(noverlap ~= abs(round(noverlap))),
    msg = 'Requires positive integer values for NFFT and NOVERLAP.';
end
if ~isempty(p),
    if (prod(size(p))>1)|(p(1,1)>1)|(p(1,1)<0),
        msg = 'Requires confidence parameter to be a scalar between 0 and 1.';
    end
end
if min(size(x))~=1,
    msg = 'Requires vector (either row or column) input.';
end
if (min(size(y))~=1)&(~isempty(y)),
    msg = 'Requires vector (either row or column) input.';
end
if (length(x)~=length(y))&(~isempty(y)),
    msg = 'Requires X and Y be the same length.';
end
